Still, sounds like opening the floodgates.

From the support articles:

Alternative app distribution is available in the countries or regions of the European Union or Japan.

Apps installed through alternative app distribution undergo a Notarization process to ensure every app meets baseline platform integrity standards, but it is up to each alternative app distributor to review apps in accordance with their own processes and policies.

Your device eligibility for apps from alternative distribution is determined using on-device processing with only an indicator of eligibility sent to Apple. To preserve your privacy, Apple does not collect your deviceʼs location.

In the European Union [iPhone and iPad]

The country or region of your Apple Account must be set to one of the countries or regions of the European Union, and you must physically be located in the European Union. 

In Japan [iPhone only]

The country or region of your Apple Account must be set to Japan, and you must physically be located in Japan.

If you leave your eligible country or region

If you leave your eligible country or region, you can continue to open and use apps that you previously installed through alternative app distribution. You can continue to update apps from alternative app distribution for up to 90 days after you leave, and you can continue using alternative app distribution to manage previously installed apps. However, you must be in your eligible country or region to install alternative app marketplaces and new apps through alternative app distribution.

Notarization for iOS and iPadOS apps is a baseline review that applies to all apps, regardless of their distribution channel, focused on platform policies for security and privacy and to maintain device integrity. Through a combination of automated checks and human review, Notarization helps ensure apps are free of known malware, viruses, or other security threats, function as promised, and don’t expose users to egregious fraud.